Typical prior art band saw blades comprise recurrent or repetitive patterns of teeth, wherein each pattern is defined by one or more groups of teeth including an unset leading tooth followed by a plurality of alternately set trailing teeth. Each recurrent pattern of teeth is typically referred to as the "pitch" pattern, "repeat" pattern or "milling" pattern of the band saw blade, since each pattern may be formed by a respective milling tool. Each pitch pattern may, in turn, define respective "set patterns" indicative of the manner in which the teeth of the pitch pattern are set. Each set pattern is defined by an unset leading tooth and a plurality of alternately set trailing teeth. For example, an "eight" tooth pitch pattern may define "three/five" set patterns. In this case, the pitch pattern comprises eight teeth, consisting of a first set pattern of three teeth, and a second set pattern of five teeth (thus the designation "three/five" set pattern). The first set pattern of three teeth is defined by a first unset leading tooth and two alternately set trailing teeth, and the second set pattern of five teeth is defined by a first unset leading tooth and four alternately set trailing teeth. Similarly, a ten tooth pitch pattern having a "three/seven" set pattern consists of a first set pattern of three teeth and a second set pattern of seven teeth, with each set pattern including an unset leading tooth followed by alternately set trailing teeth. Each unset leading tooth typically has a plane of symmetry defining the sawing plane of the blade, and which is parallel to the side surfaces at the base of the blade. The alternately set trailing teeth are typically either "right" set or "left" set, wherein each "right set" tooth is tilted or set at a predetermined angle to the right side of the plane of symmetry of the unset leading tooth, and each "left set" tooth is tilted or set at a predetermined angle to the left side of the plane of symmetry of the unset leading tooth. Typically, the first tooth in the cutting direction of the band saw blade of a particular set direction within each set pattern is referred to as the "primary" tooth, the next tooth in the set pattern of the same or like set direction is referred to as the "secondary" tooth, the next tooth in the set pattern of the same or like set direction is referred to as the "tertiary" tooth, and so on.
Certain prior art band saw blades have relatively long pitch patterns of, for example, eight or more teeth. For example, one prior art band saw blade manufactured by Amada Company, Ltd. of Japan under the designation "SVGLB 1.1/1.5" has an eight tooth pitch pattern, and a three/five set pattern. Another prior art band saw blade manufactured by Amada Company, Ltd. of Japan under the designation "3/6MVGLB" has an extended pitch pattern of approximately 23 teeth.
One drawback associated with these prior art band saw blades is that typically there is an uneven distribution of the chip load over the teeth within the relatively long pitch patterns. For example, within each group of teeth of like set direction, the secondary teeth typically bear a lesser chip load than do the corresponding primary teeth, and the tertiary teeth typically bear a substantially lesser chip load than do the corresponding secondary and primary teeth. As a result, the teeth may tend to wear unevenly and to inefficiently cut workpieces.
Yet another drawback associated with these and other prior art band saw blades, is that many of the teeth define the same pitch as do other teeth within the same pitch or set pattern. Accordingly, when cutting a workpiece, at least several of the teeth defining the same pitch may be simultaneously entering and exiting the workpiece, or several teeth defining the same pitch may be successively entering and/or exiting the workpiece, thus causing substantial vibration and noise during cutting operations.
Those skilled in the band saw blade art have recognized that a saw tooth edge having a "variable pitch" pattern may avoid the problems of excessive noise and vibrations brought about by equally spaced teeth impacting the workpieces in equal time intervals. Historically, "variable pitch" saw tooth patterns have been composed of repetitive groups of teeth arranged with progressive variations in the pitch between successive pairs of teeth in the cutting direction of the saw blade. The pitch distance is the distance between corresponding points on adjacent teeth, and typically is measured between the tips of adjacent teeth. In typical prior art variable pitch band saw blades, the variations in pitch start at the leading end of the saw blade, extend toward the trailing end of the saw blade, and are cyclical from fine to course and back to fine again. A lesser pitch distance between adjacent teeth is referred to as "fine", whereas a greater pitch distance between adjacent teeth is referred to as "coarse". Although these prior art variable pitch saw blades exhibit reduced levels of noise and vibration, these advantages frequently are achieved at the expense of reduced cutting efficiency and cutting rates of the saw blades. In particular, if these typical variable pitch patterns were applied to band saw blades having extended pitch patterns of eight or more teeth, the secondary, tertiary and possibly further successive teeth of like set direction would have significantly reduced chip loads in comparison to the preceding teeth of like set direction, thus significantly reducing the cutting efficiency and/or cutting rate of such saw blades.
Accordingly, it is an object of the present invention to overcome the above-described and other drawbacks and disadvantages of prior art band saw blades, and to provide band saw blades having extended pitch patterns of eight or more teeth that exhibit reduced noise and vibration and substantially uniform tooth loading characteristics.